Synthetic lubricants and their preparation



United States Patent @fiice 3,012,057 SYNTHETIC LUBRICANTS AND THElR PREPARATION William L. Fierce, Crystal Lake, and Walter J. Sandner,

Carpentersville, IlL, assignors to The Pure Oil Company, Chicago, 111., a corporation of Ohio No Drawing. Filed Aug. 14, 1958, Ser. No. 754,919 14 Claims. (Cl. 260-461) This invention relates to a method of preparing polysubstituted aryl phosphates having unique lubricating properties and, more particularly, to the discovery that the application of a particular processing technique, using controlled amounts of mixed phenols and phosphorus oxychloride as the reactants, results in the preparation of mixed poly-substituted aryl phosphates having low pour points, enhanced viscosity characteristics, and viscositytemperature characteristics (V.l.) greater than would be expected. More particularly, this invention relates to the discovery that the onestep reaction of a mixture of alkyl substituted phenols with phosphorus oxychloride can be controlled by varying the types and the ratios of the amounts of alkyl-substituted phenols to give products exhibiting low pour points, enhanced viscosity characteristics, and which exhibit viscosity indices greater than the corresponding tris-compounds prepared from the reaction of a single phenol with phosphorus oxychloride. Furthermore, the products qualify as synthetic lubricants for high temperature use because of their thermal stability.

Generally, neutral phosphate esters comprise three classes of compounds, namely, the trialltyl phosphates, the triaryl phosphates, and mixed alkyl-aryl phosphates. To the second class may be added the sub-class of alkylsubstituted triaryl phosphates which constitute the particular compounds with which this invention is concerned. Organo-phosphorus compounds have been known for some time and used in lubricating compositions, especially those containing a mineral oil base. Phosphate esters, such as diethyl phosphate and dioctyl phosphate, are useful as addends in lubricating oils for the purpose of imparting extreme pressure properties thereto, and as such find use in cutting oils, drawing oils and the like. Tri-ortho-cresyl phosphate, with or without a mineral oil base, is used to lubricate fine instruments and delicate mechanisms. Mixed esters of phosphoric acid, which are derived from various alcohols and phenolic compounds and constitute in part the third class mentioned above, are used in coating compositions as wetting agents, in detergents, and in textile lubricants, provided they have the proper solubility in water and oils.

In recent years there has been a steady increase in the severity of operating conditions in equipment such as aircraft, rockets, and related mechanisms. The importance of high viscosity index and thermal stability to the performance of synthetic lubricants at elevated temperatures has been stressed by many Workers in this field. However, in spite of the desirable properties of the phosphate esters and their frequent use in lubricating oil compositions and greases to impart wear resistance and inhibit corrosion, such materials have not found acceptance for use as lubricants per se without the addition of some oleaginous vehicle or other stabilizing addend.

'Moreton in United States Patent 2,566,623 recognizes the stringent requirements on such synthetic fluids as are used in the hydraulic systems of aircraft, pointing out that high viscosity index and thermal stability are imperative for proper lubrication under these severe conditions. Moreton proposes the combination of triaryl or diaryl phosphates with a suitable trialkyl phosphate to comthermal stability, low vapor pressure, lack of odor, low.

reactivity and low flammability. Such properties are required in lubricants intended for high-temperature applications. However, these triaryl phosphates have not proved acceptable as lubricants per se because of their poor viscosity-temperature characteristics. On the other hand, the trialkyl phosphates and the alkyl diaryl phospirates, which have favorable viscosity indexes, have not been used in high-temperature applications because of their poor thermal stability. None of the phosphate esters of these three classes which have been reported to date have possessed both thermal stability and favorable viscosity-temperature properties.

This invention is an improvement over the invention disclosed in application Serial No. 631,073, filed Decem: ber 28, 1956, by the present inventors. In accordance with this copending application, trialkaryl phosphates having the general formula,

wherein (15 represents a phenyl, naphthyl, anthryl or other aromatic radical, R R and R represent alkyl radicals, at least one of which contains a straight chain of not less than four carbon atoms, and n is a small whole number, possess both thermal stability and favorable viscositytemperature properties. These materials are prepared by the reaction of a substituted phenol with phosphorus oxychloride in accordance With the following equation:

In accordance with the present invention, a mixture of different alkylsubstituted phenols is used in the above reaction and the proportion of each type of phenol is adjusted to prepare unsymmetrical alkaryl phosphates having properties not recognized in the art. The products of this invention come within the foregoing general formula when ditferent alkyl groups (R R and R are attached to the phenyl groups.

It is already known in the art to prepare a cyclic alcohol ester of phosphoric acid by reacting a mixture of alcohols with phosphorus oxychloride at 0 to C. Also, mixed alkyl phenols (cresylic acids) obtained from petroleum have been reacted with phosphorus oxychloride Patented Dec. 5, 1961 p at 100 C. to prepare the corresponding triaryl phosphates. The unsymmetrical products formed by these known reactions do not share the properties of products prepared in accordance with this invention.

If a compilation is made of the pour points, viscosities and viscosity indices of various symmetrical alkyl or alkylphenyl phosphates, as in the aforementioned copending application, it will be found that the alkyl phosphates such as tridodecyl phosphate, though exhibiting high viscosity indexes, also have high pour points and low viscosities making them undesirable. Substitution of a branched-chain alkyl group, as in tris(2-ethylhexyl)phosphate, lowers the viscosity and the VI. The V1. and viscosities of alkylphenyl phosphates wherein the phenyl radical is substituted with one or more methyl groups, as in tris(o-toly-l) phosphate or t1is(3,5-dimethylpheny1) phosphate, are also too low for use as synthetic lubricants in most applications. When the alkyl group attached to the phenyl groups is increased to 4 or more carbon atoms, the alkyl aryl phosphates show proper pour points and good V.I.s and find utility as synthetic lubricants, depending on the severity of conditions to be encountered.

Thus, symmetrical compounds like tris-p-secamylphenyl phosphate, or tris-rn-tolyl phosphate are in themselves good synthetic lubricants. The respective viscosities of these compounds are about 1021 SUS and 111.2 SUS at 100 F., and their respective viscosity indices, are 38 and 14. However, there is nothing in the properties of these compounds to indicate that by reacting mixtures of m-cresol and p-sec-amylphenyl with phosphorus :oxychloride one can, by using certain mol ratios of the phenols, obtain a product having a low pour point, a reasonably high viscosity and an acceptable V.I. without loss of other physical properties. This discovery forms the basis of this invention.

Accordingly, it becomes a primarybbjectof this invention to provide a synthetic lubricant which is characterized by its thermal stability and enhanced viscosity index.

Another object of this invention is to provide a new method .of preparing a synthetic lubricant by reacting controlled amounts of certain different alkyl-substituted phenols with phosphorus oxychloride.

These and other objects of the invention will become apparent as the description proceeds.

In order to demonstrate the invention, a number of experiments were conducted using as the reactants p-secamylphenol and m-cresol in varying amounts with phosphorus oxychloride. The various samples were prepared as follows:

PRODUCT NO. A

To a 1-liter, 3-necked flask fitted with a thermometer, stirrer, dropping funnel, and ice-water bath were added 45.1 gm. (0.417 mole) of m-cresol, 95.7 gm. (0.583 mole) of p-sec-amylphenol, 250 ml. of anhydrous ether and 84 ml. (one mole plus a slight excess) of pyridine. The mixture was stirred and cooled to C. Then a solution of 51.1 gm. (0.333 mole) of phosphorus oxychloride in about 100 ml. anhydrous ether was added slowly, dropwise. The temperature was maintained between 10 and C. and the addition time was about one hour.

The mixture was stirred an additional 1 /2 to 2 hours and then allowed to warm to room temperature. After the mixture had stood overnight, it was filtered to remove pyridine hydrochloride. The ether solution was waterwashed until neutral in pH. The ether was stripped from the product by the use of heat and vacuum, leaving 97.5 gm. of a clear, viscous liquid.

PRODUCT NO. B

To a l-liter, 3-necked flask fitted with a thermometer, stirrer, dropping funnel, and ice-water bath were added 36.04 gm. (0.333 mole) of m-cresol, 109.4 gm. (0.667 mole) of p-sec-arnylphenol, 250 ml. of anhydrous ether and 84 ml. (one mole plus a slight excess) of pyridine. The mixture was stirred and cooled to 10 C. Then a solution of 51.1 gm. (0.333 mole) of phosphorus oxychloride in about ml. anhydrous ether was added slowly, dropwise. The temperature was maintained between 10 and 15 C. and the addition time was about one hour. The mixture was stirred an additional 1%. to 2 hours and then allowed to warm to room temperature. After the mixture had stood overnight, it was filtered to remove pyridine hydrochloride. The ether solution was water-washed until neutral in pH. The ether was stripped from the product by the use of heat and vacuum, leaving 126.5 of a clear, viscous liquid.

PRODUCT NO. C

To a 1-liter, 3-necked flask fitted with a thermometer, stirrer, dropping funnel, and ice-water bath were added 18.02 gm. (0.167 mole) of m-cresol, 136.9 gm. (0.833 mole) of p-sec-amylphenol, 250 m1. of anhydrous ether and 84 ml. (one mole plus a slight excess) of pyridine. The mixture was stirred and cooled to 10 C. Then a solution of 51.1 gm. 0.333 mole) of phosphorus oxychloride in about 100 ml. anhydrous ether was added slowly, dropwise. The temperature was maintained between 10 and 15 C. and the addition time was about one hour. The mixture was stirred an additional 1% to 2 hours and then allowed to warm to room temperature. After the mixture had stood overnight, it was filtered to remove pyridine hydrochloride. The ether solution was waterwashed until neutral in pH. The ether was stripped from the product by the use of heat and vacuum, leaving 154.7 gm. of a clear, viscous liquid.

PRODUCT NO. D

To a 1-liter, 3-necked flask fitted with a thermometer, stirrer, dropping funnel, and ice-water bath were added 72.1 gm. (0.667 mole) of mcresol, 54.7 gm. (0.333 mole) of p-sec-arnylphenol, 250 ml. of anhydrous ether and 84 ml. (one mole plus a slight excess) of pyridine. The mixture was stirred and cooled to 10 C. Then a solution of 51.1 gm. (0.333 mole) of phosphorus oxychloride in about 100 ml. anhydrous ether was added slowly, dropwise. The temperature was maintained between 10 and 15 C. and the addition time was about one hour The mixture was stirred an additional 1% t0 2 hours and then allowed to warm to room temperature. After the mixture had stood overnight, it was filtered to remove pyridine hydrochloride. The ether solution was water-washed until neutral in pH. The ether was stripped from the product by the use of heat and vacuum, leaving 116.7 gm. of a clear, viscous liquid.

PRODUCT NO. E

To a 1-liter, 3-necked flask fitted with a thermometer, stirrer, dropping funnel, and ice-water bath were added 54.1 gm. (0.50 mole) of m-cresol, 82.1 gm. (0.50 mole) of p-sec-amylphenol, 250 ml. of anhydrous ether and 84 ml. (one mole plus a slight excess) of pyridine. The mixture was stirred and cooled to 10 C. Then a solution of 51.1 gm. 0.333 mole) of phosphorus oxychloride in about 100 m1. anhydrous ether was added slowly, dropwise. The temperature was maintained between 10 and 15 C. and the addition time was about one hour. The mixture was stirred an additional 1% to 2 hours and then allowed to warm to room temperature. After the mixture had stood overnight, it was filtered to remove pyridine hydrochloride. The ether solution was waterwashed until neutral in pH. The ether was stripped from the'product by the use of heat and vacuum, leaving 97.7 gm. of a clear, viscous liquid.

5 The properties of the products are shown in the following table:

p-butylphenol, o-butylphenol, mbutylphenol, o-hexyl phenol, m-hexylphenol, p-hexylphenol, Z-sec-amylnaph- Table tris(o-toly1) trisp-sec Product Product Product Product Product phosphate tri-m-tolyl amyl A B C D E (TOP) phosphate phenyl phosphate Molar Proportions of Reactants:

M- resol 1. 25 1.0 O. 5 2.0 1. 5 3.0 3. 0

(O-Gresol) p-Sec-amylphenol 1. 75 2. o 2. 1. 0 1. 5 0.0 0. 0 3. 0 P0013 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1-0 Molecular Weight:

Calculated 467 480 508 424. 5 4.52. 5 368. 4 368. 37 536. 7 390 450 481 415 460.0 37

6. 62 6. 45 6. O9 7. 30 6. 84 6.3 6.1 6. 2 6. 2 6.10 Pour Point F.) 4O 35 25 20 -5 10 Viscosity SUS at:

10 495. 0 394. 8 494. O 255. 1 387. 2 190. 4 111. 2 1, 021 198. 5 166. 6 201. 7 122. b 165. 0 65. 4 55. 4 52. 6 57.2 47. 2 52. 8 40. 9 38. 6 71. 7 43 55 61 61 6O 91 14 38 It is to be observed that Products A-E were all prepared by reacting a mixture of m-cresol and p-sec-amylphenol in the ratio of 3 molar portions thereof with one molar portion of phosphorus oxychloride. However, the ratio of m-cresol and p-sec-amylphenol in the mixture was varied from 0.5 to 2.0 mol parts of m-cresol to 1.0 to 2.5 mol parts of p-sec-amylphenol.

From the results in the table, it is seen that the molecular weight of each of the Products AE very closely approximates the calculated molecular weight. However, the pour points have been improved, the viscosities are acceptable and the viscosity indices are higher in comparison with those of the three difierent symmetrical phosphates shown at the end of the table. The table shows that the percent of phosphorus in each instance follows very closely the calculated amount of phosphorus. The increases in viscosity index are unexpected when it is considered that ProductsA-E are mixed phosphates prepared from the same or similar phenols used to prepare the symmetrical compounds with which a direct comparison is made. Thus this invention provides a method of preparation and an end product which constitutes an improvement over the symmetrical phosphates. The table also compares the properties of hisp-sec-amylphenyl phosphate and di-m-tolyl-p-sec-amylphenyl phosphate.

Accordingly, this invention relates to mixed trialkylaryl phosphates of the general formula:

wherein 5 represents a phenyl, naphthyl, anthryl or other aromatic radical, R R and R represent alkyl radicals having up to 6 carbon atoms, at least one of which contains a straight chain of not less than four carbon atoms, and n has a value of l to 4, and to their use as synthetic lubricants. The products coming within the foregoing formula may be used to lubricate moving metal parts which attain high temperatures during operation or which require viscosity indices, pour points and viscosity characteristics favorable to lubrication.

Examples of phenols having a substituent alkyl group (R as above defined are, in addition to the m-cresol used in the examples, p-cresol, o-cresol, o-ethylphenol, m-ethylphenol, p-ethylphenol, m-propylphenol, o-isopropylphenol, etc.

Other examples of phenols or aromatic hydroxy com pounds coming within the above definition of the R and R groups useful in preparing the mixed esters of this invention are o-sec-amylphenol, m-sec-amyl-phenol,

thol, 3-sec-amylnaphthol, 3-sec-amylnephthol, 2-butylnaphthol, 3-butylnaphthol, 2-hexylnaphthol, 3-hexylnaphthol, 4 hexylnaphthol, etc.

The process of this invention is carried out by mixing between about 0.5 to 2.5 mole parts of the R -substituted phenols with from 2.5 to 0.5 mole parts of the R and R -substituted phenols, and reacting this mixture in the ratio of 3.0 mole parts of the mixture to about 1.0 mole part of phosphorus oxychloride, phosphorus oxybromide, phosphorus oxyiodide, or mixtures of same. A solvent such as benzene, dioxane ether, etc., may be used, together with an acceptor for hydrogen chloride, such as pyridine, ammonia, etc. The reaction is conducted in a closed vessel with means for controlling the temperature to between about 0 C. and 25 C. at approximately atmospheric pressures. After contact of the mixture for from about 1 to 3 hours, preferably with slow addition of the phosphorus oxyhalide through a dropping tunnel or other such means, the reaction mixture is allowed to come to room temperature. An ice bath can be used to control the temperature if desired. Other hydrogen halide acceptors may be used than pyridine or ammonia. Distillation can be used to remove the by-products, under vacuum if necessary, to leave the clear, viscous liquid product.

The results of this invention will be obtained as long as a mixture of phenols or naphthols as defined herein are used within the stated proportions. Gther expedients will occur to one skilled in this art to carry out the invention and the only limitations attaching to the scope thereof appear in the appended claims.

What is claimed is:

1. The method of preparing synthetic mixed phosphate lubricants having enhanced physical properties over the symmetrical counterpart which comprises reacting phosphorus oxyhalide selected from the group consisting of phosphorus oxychloride, phosphorus oxybromide and phosphorus oxyiodide with a mixture containing a compound of the formula:

wherein R is an alkyl radical containing from 1 to 3 carbon atoms, and a compound of the formula:

wherein R is an alkyl radical having from 4 to 6 carbon (1) to about 2.5 to 0.5 mol of compound (2.) and said reaction being conducted at a temperature of about 0 to 25 C. for about 1 to 3 hours.

2. The method in accordance with claim 1 in which the compound of Formula 1 is m-cresol and the compound of Formula 2 is p-sec-amylphenol.

3. The method in accordance with claim 2 in which m-cresol is mixedwith p-sec-amylphenol in the ratio of about 0.5 mol of the former to about 2.5 mols of the latter.

4. The method in accordance with claim 2 in which m-cresol is mixed with p-sec-amylphenol in the ratio of about 1.0 mol of the former to about 2.0 mols of the I latter.

5. The method in accordance with claim 2 in which m-cresol is mixed with p-sec-amylphenol in the ratio of about 1.25 mols of the former to about 1.75 mols of the latter.

6. The method in accordance with claim 2 in which m-crcsol is mixed with p-sec-amylphenol in the ratio of about 1.5 mols of the former to about 1.5 mols of the latter.

7. The method in accordance with claim 2 in which m-cresol is mixed with p-seoamylphenolin the ratio of about 2.0 mols of the former to about 1.0 mol of the latter. I

8. The product obtained by reactin' phosphorus oxyhalide selected from the group consisting of phosphorus oxychloride, phosphorus oxybromide, and phosphorus oxyiodide with a mixture containing a compound of the formula:

wherein R is an alkyl radical containing 1 to 3 carbon 8 atoms, and a compound of the formula:

wherein R is an alkyl radical having from 4 to 6 carbon atoms, in a ratio of about 1 mol of said phosphorus pound 1) to about 2.5 to 0.5 mol of compound (2) and said reaction being conducted at a temperature of about 0 to 25 C. for about 1 to 3 hours.

9. The product in accordance with claim 8 in which the compound of Formula 1 is m-cresol and the compound of Formula 2 is p-sec-amylphenol.

10. The product in accordance with claim-9 in which m-cresol is mixed with p-sec-amrylphenol in the ratio of about 0.5 mol of the former to about 2.5 mols of the latter.

11. The product in accordance with claim 9 in which m-cresol is mixed with p-sec-amylphenol in the ratio of about 1.0 mol of the former to about 2.0 mols of the latter.

12. The product in accordance with claim 9 in which m-cresol is mixed with p-sec-amylphenol in the ratio of about 1.25 mols of the former to about 1.75 mols of the latter.

13. The product in accordance with claim 9 in which m-cresol is mixed with p-sec-amylph'enol in the ratio of about 1.5 mols of the former to about 1.5 mols of the latter.

14. The product in accordance with claim 9 in which m-cresol is mixed with p-sec-amylphenol in the ratio of about 2.0 mols of the former to about 1.0 mol of the latter.

References Cited in the file of this patent UNITED STATES PATENTS 2,080,299 Beuning et al May 11, 1937 2,133,310 Shurnau Oct. 18, 1938 2,237,632 Ries Apr. 8, 1941 2,450,903 Mikeska Oct. 12, 1948 2,473,612 Shuman June 21, 1949 2,805,240 Prahl Sept. 3, 1957' 

1. THE METHOD OF PREPARING SYNTHETIC MIXED PHOSPHATE LUBRICANTS HAVING ENHANCED PHYSICAL PROPERTIES OVER THE SYMMETRICAL COUNTERPART WHICH COMPRISES REACTING PHOSPHORUS OXYHALIDE SELECTED FROM THE GROUP CONSISTING OF PHOSPHORUS OXYCHLORIDE, PHOSPHORUS OXYBROMIDE AND PHOSPHORUS OXYIODIDE WITH A MIXTURE CONTAINING A COMPOUND OF THE FORMULA: 